The present invention relates to rotary machines, and in particular, to a heat sink for a bearing in an air cycle machine.
Air cycle machines are used in environmental control systems in aircraft to condition air for delivery to an aircraft cabin. Conditioned air is air at a temperature, pressure, and humidity desirable for aircraft passenger comfort and safety. At or near ground level, the ambient air temperature and/or humidity is often sufficiently high that the air must be cooled as part of the conditioning process before being delivered to the aircraft cabin. At flight altitude, ambient air is often far cooler than desired, but at such a low pressure that it must be compressed to an acceptable pressure as part of the conditioning process. Compressing ambient air at flight altitude heats the resulting pressured air sufficiently that it must be cooled, even if the ambient air temperature is very low. Thus, under most conditions, heat must be removed from air by the air cycle machine before the air is delivered to the aircraft cabin.
To condition the air as needed, air cycle machines include a fan section, a compressor section, and a turbine section that are all mounted on a common shaft. The compressor receives partially compressed air from the aircraft and further compresses the air. The compressed air then moves through a heat exchanger and is cooled by the fan section. The air then moves through the turbine section where it is expanded for use in the aircraft, for example, for use as cabin air. The turbine section also extracts energy from the air and uses the energy to drive the fan section and the compressor section via the common shaft.
Air cycle machines also include bearings that are positioned around the common shaft. The bearings are cooled by passing a cooling air flow through a cavity that is adjacent the bearing. The cooling air flow then exits the cavity and is discharged from the air cycle machine into an ambient. The cooling air flow is limited in that it can only cool the bearing using convective heat transfer. The cooling air flow is further limited in that the cooling air flow in the cavity flows through a center of the cavity, meaning a majority of the cooling air flow does not flow across a surface of the bearing.